Methods of Fabricating Integrated Structures

ABSTRACT

Some embodiments include a memory array which has a stack of alternating first and second levels. Channel material pillars extend through the stack, and vertically-stacked memory cell strings are along the channel material pillars. A common source is under the stack and electrically coupled to the channel material pillars. The common source has conductive protective material over and directly against metal silicide, with the conductive protective material being a composition other than metal silicide. Some embodiments include methods of fabricating integrated structures.

TECHNICAL FIELD

Memory arrays and methods of fabricating integrated structures.

BACKGROUND

Memory provides data storage for electronic systems. Flash memory is onetype of memory, and has numerous uses in modern computers and devices.For instance, modern personal computers may have BIOS stored on a flashmemory chip. As another example, it is becoming increasingly common forcomputers and other devices to utilize flash memory in solid statedrives to replace conventional hard drives. As yet another example,flash memory is popular in wireless electronic devices because itenables manufacturers to support new communication protocols as theybecome standardized, and to provide the ability to remotely upgrade thedevices for enhanced features.

A typical flash memory comprises a memory array that includes a largenumber of memory cells arranged in row and column fashion. The flashmemory may be erased and reprogrammed in blocks.

NAND may be a basic architecture of flash memory. A NAND cell unitcomprises at least one selecting device coupled in series to a serialcombination of memory cells (with the serial combination commonly beingreferred to as a NAND string). Example NAND architecture is describedwith reference to a construction 2 of FIG. 1.

The construction includes a pair of memory strings 3 and 3 a. Thestrings may be identical to one another, but string 3 a is shown withless detail than string 3.

Referring to string 3, such includes a stack 10 of alternatingelectrically conductive levels 4 and electrically insulative levels 6.The levels 4 and 6 may comprise, for example, conductively-dopedpolysilicon and silicon dioxide, respectively.

A hardmask material 7 (e.g., silicon nitride) is over stack 10.

The stack 10 is over source side select gate material 12 (e.g.,conductively doped polysilicon), which is over electrically insulativeetch stop material 14 (e.g., aluminum oxide and/or silicon dioxide),which is over common source material 16 (e.g., tungsten silicide), whichis over a semiconductor base 18 (e.g., monocrystalline silicon).

Breaks are provided within the stack 10, and between the common sourcematerial 16 and the base 18, to indicate that there may be more levelsor materials than those shown in FIG. 1.

Vertically-stacked memory cells 20 are within the stack 10. The memorycells comprise control gates 22 (only some of which are labeled, andwhich correspond to regions of conductive levels 4), blocking dielectric24 (e.g., one or more of silicon nitride, silicon dioxide, hafniumoxide, zirconium oxide, etc.), and charge storage material 26 (e.g.,material suitable for utilization in floating gates or charge-trappingstructures; such as, for example, one or more of silicon, siliconnitride, nanodots, etc.).

A channel material 28 (e.g., polysilicon) forms a pillar extendingthrough the stack 10 to the common source material 16.

Gate dielectric material 30 (e.g., silicon dioxide) is between thechannel material 28 and the charge storage material 26 of the memorycells 20.

The channel material connects to a drain side select device 32, which inturn connects to a data line (e.g., a bitline) 34.

Referring to string 3 a, such also includes the stack 10, hardmask 7,source side select gate material 12, and etch stop material 14. Further,string 3 a is shown to comprise the channel material 28 and gatedielectric material 30, with the channel material 28 extending to thecommon source material 16. The string 3 a comprises memory cells of thetype shown as cells 20 of string 3, but such memory cells are shown in amore simplified view in string 3 a. A drain side select device (likedevice 32) and data line (like line 34) would also be electricallycoupled with channel material of string 3 a, but such are not shown.

A prior art problem is shown in locations were channel material 28 ofstrings 3 and 3 a interfaces with common source material 16.Specifically, the common source material may react with oxygen to forman oxide 36 which is difficult to remove. The oxide 36 mayproblematically reduce the quality of the electrical contact betweenmaterials 16 and 28; which can impair performance of devices, and insome cases render devices non-operational.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is diagrammatic cross-sectional view illustrating a portion of aprior art memory array.

FIGS. 2-5 are diagrammatic cross-sectional views of a portion of asemiconductor construction illustrating process stages of an exampleembodiment method of fabricating integrated structures. FIG. 5A is a topview of the construction of FIG. 5, and the cross-sectional view of FIG.5 is along the line 5-5 of FIG. 5A.

FIG. 6 is a diagrammatic cross-sectional view of an example embodimentconstruction alternative to that of FIG. 5. FIG. 6A is a top view of theconstruction of FIG. 6, and the cross-sectional view of FIG. 6 is alongthe line 6-6 of FIG. 6A.

FIGS. 7-10 are diagrammatic cross-sectional views of a semiconductorconstruction illustrating process stages of another example embodimentmethod of fabricating integrated structures.

FIGS. 11 and 12 are diagrammatic cross-sectional views of asemiconductor construction illustrating process stages of anotherexample embodiment method of fabricating integrated structures. Theprocess stage of FIG. 11 may follow either the process stage of FIG. 2or the process stage of FIG. 9 in some embodiments.

FIGS. 13-15 are diagrammatic cross-sectional views of a portion of asemiconductor construction illustrating process stages of anotherexample embodiment method of fabricating integrated structures.

FIG. 16 is a diagrammatic cross-sectional view of a portion of asemiconductor construction comprising an example embodiment memoryarray.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In some embodiments, the invention includes new memory architectureshaving improved contact between channel region material and commonsource material as compared to conventional devices (such as, forexample, the prior art devices of FIG. 1). In some embodiments, theinvention includes new methods of fabricating integrated structures.Example embodiments are described with reference to FIGS. 2-16.

Referring to FIG. 2, a construction 50 is shown to comprise sourcematerial 52 over a base 54. The source material may be incorporated intoa common source analogous to the common source 16 discussed above withreference to FIG. 1. The source material comprises oxygen-sensitivemetal silicide, and in some embodiments may comprise, consistessentially of, or consist of tungsten silicide. The oxygen-sensitivemetal silicide reacts with oxygen to form an undesired composition(e.g., an oxide) under the processing conditions utilized forfabricating vertically-stacked circuitry (such as, for example,vertically-stacked memory cells analogous to those of FIG. 1).

Base 54 may comprise semiconductor material, and may be analogous to thebase 18 discussed above with reference to FIG. 1. For instance, base 54may comprise, consist essentially of, or consist of monocrystallinesilicon. In some embodiments, base 54 may be considered to comprise asemiconductor substrate. The term “semiconductor substrate” means anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductor substratesdescribed above. In some embodiments, base 54 may correspond to asemiconductor substrate containing one or more materials associated withintegrated circuit fabrication. Some of the materials may be under theshown region of base 54 and/or may be laterally adjacent the shownregion of base 54; and may correspond to, for example, one or more ofrefractory metal materials, barrier materials, diffusion materials,insulator materials, etc.

The oxygen-sensitive source material 52 has an upper surface 53.

Referring to FIG. 3, protective material 56 is formed over and directlyagainst the upper surface 53 of oxygen-sensitive material 52. Theprotective material is electrically conductive, and the two materials 52and 56 may be together considered to form a conductor 58 (e.g., anelectrically conductive line).

In some embodiments, protective material 56 may react with oxygen toform an oxide which is readily removed by wet or dry etch and, onceremoved, appreciable oxide may not grow back for a substantial period oftime (for instance, more than 2 hours). In contrast, material 52 mayreact with oxygen almost immediately to form problematic oxide, and suchproblematic oxide may be difficult to remove. In some embodiments,material 56 may be stable relative to exposure to oxygen (e.g., may notreact with oxygen to form undesired oxide under fabrication conditionsutilized for forming vertically-stacked integrated structures; such as,for example, vertically-stacked memory cells analogous to thosedescribed above with reference to FIG. 1).

Protective material 56 may comprise any suitable electrically conductivecomposition. For instance, in some embodiments material 56 may compriseconductively-doped semiconductor material (e.g., conductively-dopedsilicon, germanium, etc.), metal, etc. The semiconductor material may beconductively-doped with either n-type dopant or p-type dopant. P-typedopant may be particularly advantageous in some embodiments.

The particular embodiment of FIG. 3 may comprise a protective material56 corresponding to conductively-doped semiconductor material (e.g.,silicon), with such semiconductor material being formed by physicalvapor deposition in a process which is in situ relative to the processutilized to form oxygen-sensitive metal silicide 52. Accordingly, theupper surface 53 of material 52 is never exposed to oxygen. The in situformation of conductor 58 may comprise utilization of a depositionapparatus which enables physical vapor deposition of metal silicide 52in one chamber, followed by physical vapor deposition of material 56 ineither the same chamber, or in another chamber, without breaking vacuumor otherwise exposing the upper surface 53 of material 52 to oxygen.

Protective material 56 may comprise any suitable thickness. In someembodiments, protective material 56 may correspond to polysilicon formedto a thickness within a range of from about 200 Å to about 1000 Å.

Referring to FIG. 4, a structure 60 is formed over conductor 58. In theshown embodiment, structure 60 comprises the stack 10 of alternatingfirst and second levels 4 and 6 discussed above with reference to FIG. 1(i.e., conductive levels 4 and insulative levels 6), comprises anopening 62 extending through the stack, and comprises repeatingvertically-stacked electrical components 20 along sidewalls of theopening (with such electrical components 20 corresponding to memorycells of the type described above with reference to FIG. 1). Gatedielectric material 30 is also formed along sidewalls of the opening 62.The shown embodiment comprises the materials 7, 12 and 14 discussedabove with reference to FIG. 1. The embodiment of FIG. 4 is one ofnumerous embodiments that may utilize the conductor 58. In otherembodiments, other vertically-stacked electrical components may beutilized in addition to, or instead of, the memory cells 20. In someembodiments, other types of memory cells may be utilized instead of theparticular memory cells 20 described above with reference to FIG. 1. Forinstance, the memory cells may be configured to have blocking dielectric(24 of FIG. 1) and/or charge-trapping material (26 of FIG. 1) in adifferent configuration than shown in FIG. 1.

Referring to FIG. 5, channel material 28 is formed within opening 62,and is configured as a vertically-extending pillar within such opening.The channel material is directly against protective material 56 at abottom of the opening. The processing stages of FIGS. 4 and FIGS. 5 mayexpose a bottom of opening 62 to oxygen prior to formation of channelmaterial 28 within such opening. However, protective material 56 eitherreacts with oxygen too slowly to form appreciable oxide under theconditions in which it is exposed at the bottom of the opening, doesn'treact with oxygen, or reacts to form readily removed oxide. In anyevent, the problematic oxide 36 of FIG. 1 may be avoided. The channelmaterial 28 may comprise any suitable material, and in some embodimentsmay comprise silicon.

The conductor 58 forms a common source in the embodiment of FIG. 5. Suchcommon source extends beneath a memory string 64 analogous to thestrings 3 and 3 a of FIG. 1. Such memory string may be one of numerousmemory strings of a memory array, and the common source may extend undersome or all of the strings of the memory array.

In some embodiments, one or both of materials 52 and 56 of conductor 58may be heavily doped, and thermal processing may be utilized toout-diffuse dopant from materials of conductor 58 into a lower region ofchannel material 28 to heavily dope such lower region of the channelmaterial. The heavy doping within the lower region of the channelmaterial may enable desired current generation during operation of thechannel material, and may provide a desired low resistance contactbetween the channel material and the conductor 58. In some embodiments,the out-diffusion of dopant from conductor 58 may create a heavily-dopedlower region of channel material 28 extending to about a boundarydiagrammatically illustrated with dashed line 61 in FIG. 5.

In some embodiments, material 56 of conductor 58 may be silicon which isdoped in situ to a desired heavy doping. In some embodiments, metalsilicide 52 may contain heavy doping, and out-diffusion from material 52may be utilized to enhance doping within silicon-containing material 56to provide desired heavy doping suitable for material 56 to have desiredconductivity.

The channel material 28 of FIG. 5 forms a solid conductive pillar withinopening 62, as can be seen in a top view of FIG. 5A. In otherembodiments, the channel material may form a hollow pillar within theopening, as shown in FIGS. 6 and 6A.

The embodiment of FIGS. 2 and 3 forms protective material 56 in situwith oxygen-sensitive metal silicide 52 so that oxide never forms acrossan upper surface 53 of material 52. In other embodiments, oxide may formacross an upper surface of material 52, and may be removed prior toformation of protective material 56. An example embodiment in whichoxide is removed is described with reference to FIGS. 7-10.

Referring to FIG. 7, a construction 50 a is shown comprisingoxygen-sensitive metal silicide 52 over base 54. The metal silicide maybe formed by physical vapor deposition or any other suitable method.

Referring to FIG. 8, metal silicide 52 is exposed to oxygen (forinstance, exposed to ambient), and accordingly an oxide 68 forms acrossan upper surface of metal silicide 52. In the shown embodiment, theoxide forms across an entirety of the upper surface. In otherembodiments only a portion of such upper surface may be exposed tooxygen, and accordingly the oxide 68 may form across only a portion ofthe upper surface. Regardless, oxide 68 forms across a region of theupper surface of metal silicide 52.

Referring to FIG. 9, oxide 68 (FIG. 8) is removed from over the metalsilicide 52 to expose a clean surface 69 of the metal silicide. Theoxide may be removed utilizing any suitable processing; and in someembodiments may be removed by exposure to one or more reductants. Suchreductants may comprise, for example, H₂, NH₃/NF₃, etc.

Referring to FIG. 10, protective material 56 is formed on the cleansurface 69 of metal silicide 52 to form the conductor 58. The protectivematerial may be formed with processing that does not expose the cleansurface 69 to air (or any other source of oxygen) in order to avoidproblematic oxide formation. The protective material 56 may be formedutilizing any suitable method, including, for example, methodologydiscussed above with reference to FIG. 3, or methodology discussed belowwith reference to other embodiments. Accordingly, in some embodimentsprotective material 56 of FIG. 10 may comprise conductively-dopedsemiconductor material (e.g., silicon, germanium, etc.), and in someembodiments protective material 56 of FIG. 10 may comprise metal. Theconstruction 50 a of FIG. 10 may be subjected to subsequent processinganalogous to that of FIGS. 4 and 5 (or that of FIGS. 4 and 6) to formvertically-stacked electrical components over the conductor 58; and tohave a solid or hollow channel material pillar in contact with material56.

The embodiment of FIG. 3 formed an entirety of semiconductor-containingprotective material 56 in a single deposition. In other embodiments,material 56 may be formed utilizing two or more depositions ofsemiconductor material. An example embodiment in which the protectivematerial is formed utilizing multiple depositions is described withreference to FIGS. 11 and 12.

Referring to FIG. 11, a construction 50 b is shown at a processing stagesubsequent to that of FIG. 2. A first portion 70 of protective material56 is formed on an upper surface 73 of metal silicide 52 by physicalvapor deposition of semiconductor material (e.g., silicon). The firstportion may comprise any suitable thickness. In some exampleembodiments, portion 70 may comprise a thickness of less than or equalto about 30 Å. In some example embodiments, portion 70 may comprise athickness of from about 30 Å to about 300 Å. The first portion may ormay not be conductively doped at the process stage of FIG. 11.

Referring to FIG. 12, a second portion 72 of protective material 56 isformed over the first portion. The second portion may be formedutilizing any suitable method, including, for example, one or more ofepitaxial growth, chemical vapor deposition, atomic layer deposition,etc. In some embodiments, the second portion 72 is formed with adifferent method than that utilized to form the first portion 70; andspecifically may be formed by a method which is faster and/or otherwisemore cost-effective than the method utilized to form the first portion70. The second portion 72 may or may not be conductively-dopedas-formed. For instance, in some embodiments, dopant may be providedwithin the second portion after deposition of the second portion usingout-diffusion of dopant from one or both of metal silicide 52 and firstportion 70; in some embodiments second portion 72 may be doped duringdeposition of the second portion; and in some embodiments second portion72 may be doped using an implant. Similarly, in some embodiments firstportion 70 may be doped after deposition of the first portion usingout-diffusion of dopant from one or both of metal silicide 52 and thesecond portion 72; in some embodiments may be doped during deposition ofthe first portion; and in some embodiments may be doped using animplant.

The first and second portions 70 and 72 may have any suitablethicknesses. In some embodiments, portion 70 may be formed to thicknessof from about 30 Å to about 300 Å, and portion 72 may be formed tothickness of from about 200 Å to about 1000 Å.

Although the first and second portions are shown comprising a samecomposition 56 as one another, in other embodiments the first and secondportions may comprise different compositions relative to one another.For instance, one of the first and second portions may primarilycomprise germanium while the other primarily comprises silicon.

The portions 70 and 72 of protective material 56, together with metalsilicide 52, form a conductor 58. The construction 50 b of FIG. 12 maybe subjected to subsequent processing analogous to that of FIGS. 4 and 5(or that of FIGS. 4 and 6) to form vertically-stacked electricalcomponents over the conductor 58; and to have a solid or hollow channelmaterial pillar in contact with material 56.

FIGS. 13-15 illustrate an example embodiment in which protectivematerial 56 comprises metal.

Referring to FIG. 13, a construction 50 c is shown at a processing stageidentical to that described above with reference to FIG. 2. Theconstruction comprises oxygen-sensitive metal silicide 52 over base 54.

Referring to FIG. 14, metal-containing protective material 56 is formedover and directly against an upper surface 53 of metal silicide 52.Metal of material 56 may be referred to as a second metal to distinguishit from the first metal of metal silicide 52. The first and secondmetals may be the same as one another in some embodiments, and may bedifferent from one another in other embodiments. For instance, in someembodiments metal silicide 52 may comprise, consist essentially of, orconsist of tungsten silicide; and protective material 56 may comprise,consist essentially of, or consist of tungsten.

Metal-containing protective material 56 may be formed by physical vapordeposition in a process which is in situ relative to the processutilized to form oxygen-sensitive metal silicide 52. Accordingly, anupper of material 52 is never exposed to oxygen. The in situ formationof conductor 58 may comprise utilization of a deposition apparatus whichenables physical vapor deposition of metal silicide 52 in one chamber,followed by physical vapor deposition of metal-containing material 56 ineither the same chamber, or in another chamber, without breaking vacuumor otherwise exposing the upper surface 53 of material 52 to oxygen.

The protective material 56 may be formed to any suitable thickness, andin some embodiments may be formed to thickness of from about 100 Å toabout 1000 Å.

The protective material 56 and metal silicide 52 together form aconductor 58.

Referring to FIG. 15, subsequent processing analogous to that describedabove with reference to FIGS. 4 and 5 may be utilized to formvertically-stacked electrical components over conductor 58 ofconstruction 50 c. The channel material 28 extends through the stackedelectrical components and to the conductor 58. In some embodiments,channel material 28 may directly contact an upper surface of material 56analogously to the construction shown in FIG. 5. In other embodiments,channel material may be spaced from protective material 56 by anintervening material 80 as shown in FIG. 15. For instance, in someembodiments channel material 28 may comprise silicon, and such siliconmay react with an upper surface of metal-containing material 56 to forma metal silicide. In particular embodiments, material 56 may comprise,consist essentially of, or consist of tungsten; and material 80 maycomprise, consist essentially of, or consist of tungsten silicide.

In the embodiment of FIG. 15, metal silicide 52 may be provided withdopant dispersed therein, and such dopant may be out-diffused throughmaterials 56 and 80, and into a lower region of channel material 28 toheavily dope such lower region in a manner analogous to theout-diffusion discussed above with reference to FIG. 5.

Although the embodiment of FIG. 15 shows channel material 28 as a solidpillar, in other embodiments the channel material may be a hollow pillaranalogous to the hollow pillar shown in FIG. 6.

In some embodiments, the conductors 58 of the above-discussedembodiments may be utilized as a common source in memory arrays. FIG. 16shows a construction 100 comprising a memory array 102 containingmultiple NAND strings 103-105 associated with a common sourcecorresponding to conductor 58. The memory strings may compriseembodiments in accordance with those described above with reference toFIGS. 2-15. Although the channel material pillars of FIG. 16 are shownas solid pillars, in other embodiments they may be hollow pillars of thetype shown in FIG. 6.

The structures and arrays discussed above may be incorporated intoelectronic systems. Such electronic systems may be used in, for example,memory modules, device drivers, power modules, communication modems,processor modules, and application-specific modules, and may includemultilayer, multichip modules. The electronic systems may be any of abroad range of systems, such as, for example, clocks, televisions, cellphones, personal computers, automobiles, industrial control systems,aircraft, etc.

Unless specified otherwise, the various materials, substances,compositions, etc. described herein may be formed with any suitablemethodologies, either now known or yet to be developed, including, forexample, atomic layer deposition (ALD), chemical vapor deposition (CVD),physical vapor deposition (PVD), etc.

The particular orientation of the various embodiments in the drawings isfor illustrative purposes only, and the embodiments may be rotatedrelative to the shown orientations in some applications. The descriptionprovided herein, and the claims that follow, pertain to any structuresthat have the described relationships between various features,regardless of whether the structures are in the particular orientationof the drawings, or are rotated relative to such orientation.

The cross-sectional views of the accompanying illustrations only showfeatures within the planes of the cross-sections, and do not showmaterials behind the planes of the cross-sections in order to simplifythe drawings.

When a structure is referred to above as being “on” or “against” anotherstructure, it can be directly on the other structure or interveningstructures may also be present. In contrast, when a structure isreferred to as being “directly on” or “directly against” anotherstructure, there are no intervening structures present. When a structureis referred to as being “connected” or “coupled” to another structure,it can be directly connected or coupled to the other structure, orintervening structures may be present. In contrast, when a structure isreferred to as being “directly connected” or “directly coupled” toanother structure, there are no intervening structures present.

Some embodiments include a memory array which has a stack of alternatingfirst and second levels. Channel material pillars extend through thestack, and vertically-stacked memory cell strings are along the channelmaterial pillars. A common source is under the stack and electricallycoupled to the channel material pillars. The common source comprisesconductive protective material over and directly against metal silicide.The conductive protective material comprises a composition other thanmetal silicide.

Some embodiments include a method of fabricating integrated structures.A conductor is formed to comprise conductive protective material overand directly against oxygen-sensitive metal silicide. A structure isformed over the conductor. The structure comprises a stack ofalternating first and second levels, an opening extending through thestack to the conductive protective material, and repeatingvertically-stacked electrical components along the stack at sidewalls ofthe opening. Channel material is formed within the opening and directlyagainst the conductive protective material.

Some embodiments include a method of fabricating integrated structures.Conductive protective material is formed over an oxygen-sensitive metalsilicide. A stack of alternating first and second levels is formed overthe conductive protective material. An opening is formed to extendthrough the stack to the conductive protective material. Channelmaterial is formed within the opening and directly against theconductive protective material. Dopant is out-diffused from one or bothof the conductive protective material and the metal silicide into abottom region of the silicon-containing channel material.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

1-28. (canceled)
 29. A method of fabricating integrated structures, comprising: forming a conductive protective material over and directly against oxygen-sensitive metal silicide; forming a stack of alternating first and second levels over the conductive protective material, the stack comprising an opening extending to the conductive protective material; and forming a pillar of conductive material within the opening and directly against the conductive protective material.
 30. The method of claim 29 wherein the oxygen-sensitive metal silicide comprises tungsten silicide.
 31. The method of claim 29 wherein the forming of the conductive protective material comprises physical vapor deposition.
 32. The method of claim 29 wherein the pillar of the conductive material comprises channel material.
 33. The method of claim 32 wherein the channel material comprises silicon.
 34. The method of claim 32 wherein the channel material comprises polysilicon.
 35. A method of fabricating integrated structures, comprising: forming protective material over an oxygen-sensitive metal silicide, the forming of the conductive protective material comprising multiple depositions; forming a stack of alternating first and second levels over the conductive protective material; forming an opening through the stack to the conductive protective material; and forming a pillar of conductive material within the opening and directly against the protective material.
 36. The method of claim 35 wherein the multiple depositions comprises more than two depositions.
 37. The method of claim 35 wherein the multiple depositions creates the protective material comprising a first portion below a second portion.
 38. The method of claim 37 wherein the second portion of the protective material is thicker than the first portion of the protective material.
 39. The method of claim 37 wherein the second portion of the protective material is formed utilizing a different method than the first portion of the protective material.
 40. The method of claim 37 wherein the second portion of the protective material comprises a different composition than the first portion of the protective material.
 41. The method of claim 37 wherein at least one of the first and second portions of the protective material is originally formed non-conductive.
 42. The method of claim 37 wherein both of the first and second portions of the protective material are originally formed non-conductive.
 43. The method of claim 42 wherein at least one portion of the originally-formed protective materials is subsequently doped with conductive material.
 44. The method of claim 42 wherein both portions of the originally-formed protective material are subsequently doped with conductive material. 